Choosing the right skin product is like picking the perfect mate: Look for the good things they offer, but be aware of red flags.

That's because certain ingredients in skin treatments may irritate or damage your skin, write Mehmet Oz, MD, and Michael Roizen, MD, in their new book, YOU: Being Beautiful -- The Owner's Manual to Inner and Outer Beauty. If your skin's been acting up, check your products' labels for any of these five red flags:

1. Smell-good fragrances: They may tickle your nose, but these little molecules set off allergic reactions in up to 14 percent of people.
2. Suds-making sodium lauryl sulfate: It creates bubbles and foam in shampoos and cleansers but could strip your skin of lipids -- natural moisturizers that smooth and soften it. The result: irritation and dryness. (Get the lowdown on what to look for in moisturizing products.)
   
3. Two preservatives: imidazolidinyl urea and diazolidinyl urea. They're used to prevent bacterial growth but can also cause contact dermatitis. (What does contact dermatitis look like? Read this tip.)
   
4. MEA, TEA: They're common stabilizers, but when exposed to air, they form potentially irritating substances, tend to clog pores, and can create blackheads. (Is your skin acne-prone? Try these pimple-preventing strategies.)
5. DMAE: This so-called "instant facelift" ingredient in wrinkle creams works by damaging cells, which causes slight swelling. Yes, the swelling smoothes out wrinkles temporarily, but that doesn't mean it's good for your skin. (Here's a quick rundown of wrinkle smoothers and fillers that really do work.)

Get more beautiful-inside-and-out tips and tricks from YOU: Being Beautiful -- The Owner's Manual to Inner and Outer Beauty.

YOU: Being Beautiful -- The Owner's Manual to Inner and Outer Beauty. Oz, M. C., Roizen, M. F., New York: Simon & Schuster, 2008.